Two things that decrease a population

War and disease are two major ones

Two things that might cause a decrease in population might be environmental hazards, or a spread of a disease.

Hope I helped! :)

During the paleolithic, hominins grouped together in small societies such as bands, and subsisted by gathering  plants  and fishing, hunting or scavenging wild  animals. the paleolithic is characterized by the use of knapped stone tools, although at the time humans also used  wood  and bone tools.